RUNX1/CBFbeta is a key regulator of normal hematopoiesis that is frequently involved in leukemia. Rearrangements involving the CBF family account for approximately 25% of de novo myeloid leukemias and 22% of pediatric lymphoblastic leukemias. The overall objective of the proposed study is to understand gene expression that is determined by leukemia-associated translocation fusion proteins of the RUNX1/CBFbeta transcription factor, and to evaluate the role of these regulated genes in normal and leukemic stem cell self-renewal, survival and differentiation. The fusion proteins we will focus on are the t(8;21) encoding AML1-ETO, t(3;21) encoding AML1-EVI1, and the inv16/t(16;16) encoding CBFbeta- MYH11. These will be expressed in human HSPC by lentiviral transduction. Controls will include a lentivirus lacking a transgene as well as a lentivirus expressing RUNX1. Differentially expressed target genes will be validated using human HSPC expressing either AML1-ETO or CBFp-MYH11 that have acquired enhanced self-renewal properties due to the oncogene expression. Clinical samples from AML patients expressing a RUNX-fusion oncogene will also be analyzed for expression of the identified genes (Aim 1). The specific contribution of identified target genes to HSPC function will be evaluated by over-expressing genes that are repressed by the fusion proteins, and conversely by knocking-down those genes that become upregulated upon fusion protein expression, using lentiviral transduction of the human HSPC that express these oncogenes and that self-renew in vitro. Primary human HSPC will be similarly transduced to determine the contribution of the targeted gene to normal stem cell function (Aim 2). Understanding the modulation of the self-renewal process by these fusion proteins could give insight into the normal mechanisms of self-renewal employed by the stem cell. [unreadable] [unreadable]